Flowmeter



` F. J. WIEGAND..

Filed Jan. 14, 1943 FLQWMETER INVENTOR FRA Nc/s d. W/:GA/vn.

4 /a a if ATTORNEY Patented ug. 20, 1946 s PATENroF FLOWMETER Francis J. Wiegand. Ridgewood, N. J., assignor to' .Wright Aeronautical Corporation, a corporation of New York 1 Application January 14, 1943, seria1N.472,409

, l 3 Claims.l

This invention relates to measuring apparatus and is particularly concerned with apparatus for transforming small pressure differentials into larger and more useful pressure differentials.

A typical'application of this invention is for measuring small low rates of fluid iiow by means of a venturi. Inaccordancewith this invention, the small dili'erential pressure produced by a low rate of iiuid flow through a venturi is transformed into 'a larger pressure differential. Thus, the apparatus could be used for measuring fuel flow to an internal combustion engine. art, in order to transform a small pressure differential into a larger pressure diierential, it is common practice to do so by using electric er pneumatic relays which control an external source of energy. It is an object ofthis invention to transform the small differential pressure to be measured into a larger pressure differential without the use of any external Source of energy.

Specifically, this invention comprises a diaphragm system consisting of a relatively large diaphragm subjected to a pressure diiferential responsive to the condition to be measured and a second diaphragm mechanically connected to the rst diaphragm for movement therewith. The mechanical connection between the diaphragms operates a valve for controlling the transmission of pressure from the high pressure side of the larger diaphragm to the high pressure side of the smaller diaphragm to balance the diaphragm system. ,y

Other objects of thisinventionwill become apparent in reading the annexed detailed description in connection rwith the drawing, in which:

Fig. 1 isa diagrammatic view of the invention; and l l Fig. 2 is a diagrammatic view of a modification. Referring to the drawing, a conduit I is provided with a Venturi throat I2 for metering the flow of the fluid through the conduit. Conduits I4 and I6 connect the Venturi throat I2 and bar- 36 in the wall of chamber 20 and this openingl chamber 20 to chamber 32. Accordingly, the dia- In the prior phragm 26 is subjected to a force to the right, as .seen in the drawing, to balance the Vvforce ,act-- ing on diaphragm 274, the force acting on elia-` phragm 26 being equal to the pressure differentialv between the pressure in chamber 32 and atmos; pheric pressure or other balance pressure A small flow in the conduit I0 will subject the diaphragm 24 to a small force'to the left to open l the valve 30. Pressure will then be transmitted from chamber 2!) to chamber 32 until the diaphragm 26 is subjected tov a suiilcient pressureY differential to balance the'pressure differential acting on diaphragm 24.- Upon an increase in iiow in conduit ,I0, the pressure differential on diaphragm 24 increases to further open the valve 30 until the pressure differential acting on the dia-` phragm 26'has increased suiiiciently to again balance the system Similarly, a decrease in flow through the conduit I0 results in a decrease in the pressure differential acting on the diaphragm rel I3 with chambers I8 and 20, respectively.

These chambers are formed within a housing 22 by a flexible diaphragm 24. Thus, the diaphragm 24 is urged to the left, as seen on the drawing, by a force proportional to the magnitude of. the flow through conduit I 0. A second diaphragm 26 'is mechanically connected to the diaphragm .24 by a stem 28provided with av poppet valvef30. This diaphragm 26 separates the chamber 32.from the atmosphere or other balance pressure and a restrictive outlet 34 provides a drain bleed for the chambertothe atmosphere orother vent pressure. The stem 28'pas`s'es througli'an'opening 24v thereby moving the `valve 30 in a closing direction. The bleed 34 inthe chamber 32 then per. mits a reduction in the pressure in this chamber until the pressure diiferential acting on `diaphragm ,26 has been reduced 'suiiiciently to again balance the diaphragm system.` Thus, the valve 3i|will assume a position to maintain the correct.v to balance 4the d-iapressure in the chamber 32 phragmsystem.

When the diaphragm system is balanced, the

pressure differential acting on thesmaller diaphragm 26 is necessarily largerthan the pressure differential acting on the larger diaphragm 24 in proportion to-the ratio of the areas -of these diaphragms. Therefore,V since the pressure differential acting on the diaphragm 24 is a measure of the iiow through the conduit I 0,-the larger-y and more useful pressure differential acting on the diaphragm. 26 is also av measure of the` flow through4 conduit` I U. Accordingly, this larger pres.-

' sure Vdifferential may be used to operate an indicator calibrated so as to indicate the flowinconv.

duit I0. -Y

VVAt this point 1tV shomd be noted that the reative sizeof the diaphragms must be correctly pro- Y portionedin View of thelmagnitude of the pressure diierential acting on the diaphragm 24 and in View of lthe relative magnitude of these pres-j sures lasicompared 4to the atmospheric pressure .Y Aor other balance pressure to which the diaphragm is subjected. Thus, if the diaphragm'ZE is too Fler.

small or the pressure differential on the diaphragm 24 Vis too large, it will be impossible to develop sufficient pressure within the chamber 32 to balance the diaphragm system even though valve 30 is fully open. Also, with atmospheric pressure on one side of diaphragm 26 it i-s essential that the pressures on both sides of diaphragm 24 be greater than atmospheric pressure, other- Wise it Will be impossible to balance the dia-5 phragm system. However, if the right side of the diaphragm 26 is subjected to other than atmos-.l pheric pressure, it is only necessary that the pres-1l sures acting on diaphragm 24 be greater'tlfianA this other pressure. As previously stated, Ythis in vention may be used for measuring fuel flow toan internal combustion engine. In such case, a fuel pressure of pounds per square inch is typical.

of example. and is not to be construed as limiting the use of the invention.

In Fig. l the amplified pressure differential acting on the diaphragm 26 is used for operating The pres-v a remote Selsyn motor type indicator. y sure from the chamber- 32 is transmitted vby a pipe 31 to a Siylphon bellows38 so that this bellows Vis subjected to the same pressure diiierential pei unit-effective area as diaphragm 26. The bellows 38 nis connected to thegvrotor of a Selsyn transmitter -40 bypa'rack 42 and a pinion 44. Selsyn transmitter 40 is connected to a remote Selsyn receiver 46 in ther conventional mannen Thus, the Selsyn receiver ig responsive tothe pressure differential acting' on the diaphragm 26 so that the rotor of the Selsyn receiver may drive an indicator 4 8 calibrated to read the ow in conduit I0.

Fig. 2 isa mcdincation of the system of Fig,y 1l

illustrating al different type of indicating means responsive to the differentialpressure acting on the diaphragm 2,6. That portion of Fig. 2 similarY tovFig'. 1 has beendesignated by similar reference numerals and no further description of this portion of the apparatus is deemed necessary. In

this modification the chamber 32 is connected to a chamberjSU-by a conduit 5,2. lA flexible dia? phrag'my 54v separates this chamber fromv the at lmosphere sothat this diaphragm'is subjected to the same pressure differential per unit area as that acting against diaphragm. 26. A link arm 56' connects the diaphragm 45'4 to a liexibleV cantilever beam 58 lso that the deflection yof this beam isl proportional to the pressure differential acting against d iaphragms'Z and 54. Y v' A pair of conventional granular` carbon type resistances 60 and` 62 are mounted on opposite sides of the beam 58 so that deflection of the`l` beam isA operative thru insulating arms 59 and' 6l to increase one of these resistances and decrease the other resistance. These resistances form a pair of' arms of a conventional Wheatstone bridge circuit 64. A galvanometer 66 or other indicator is connected across this bridgeV and may be cali` brated to read the iiow invv conduit I0, since the deflection ofY beam 58 is proportional tothe pres--Y sure differential acting against the diaphragm 2'6. By'providing a pair of resistances 60 and B2op` The ` k However, this pressure is only mentionedfby wayy The apparatus has been illustrated and described in connection with the pressure differential created by a fluid iiowing through a venturi.

However, the apparatus is of general application f and can be used wherever amplification of a small pressure differential is desired.

While I have described my invention in detail in its present4 preferred embodiment, it will be obvious to'those'skilled in, theart,y after understanding my invention, that various changes and modifications may be made therein Without departing from the spirit or scope thereof. I aim the appended claims to cover all rsuch modiications and changes. v

' I'cl'aimas my invention: `v c l'. vInV apparatusk for transforming apsmall pressure differential into a larger pressure differential, the individualpressures of. said small pressure differential both being greater than atmospheric pressure, a housing, a rst movable mem ber dividing said housing into a pair of opposedv chambers, means for subjecting said memberand, chambers to said small pressure differential, the wall ofthe high pressure chamber removedl fromV said member having an opening therethrough into a third chamber, a second movable member in said third chamber connectedjto said Virst' member for joint movement therewith by means;

extending through said opening, said sectmdY ,member being ofgsmaller effective varea than 'said't '-'rst member, a Vvalve element Aformed on saidconnecting means for cooperation with saidopening, 'the other side of said second member being subjected to atmospheric pressure, a. restricted vent for said third chamber, and meansv responsive to the pressurerdifferential across said second member.

2. Apparatus for transforming a small fluid. pressure dilferentialinto a larger pressure diiferential comprising a housing, a first movablemember dividing said housing into a pair of opposed chambers, means for subjecting said chambers and consequently said movable member to said, small pressure differentiaLa `third chamberfsep-` arated from the high pressure chambenof, said pair of chambers by a fixed partition, a' second.r

positely responsive to the deflection of the beam 58 insteadV of justr one resistance, the effect of ambientY temperature surrounding the apparatus' is eliminated. If'V the apparatus is being used to measure fuel flow to an internalcombustion en` gine elimination of the effect of ambient temperature is q uite important because 0f the varia` ent Y operatingy conditions,

Y tion in temperaturev of the engine under differmovableA member of smallereffectivev area than said iirst member anddisposed across saidthird chamber, :means extending through, an yopening, in vsaid partition and connecting said membersV i for 'joint movement;v avvalve element Ymoi'fabley byn said connecting meansl and cooperating withklsa'id opening for `controlling the transmission Vo fj pressure from said hig'hpressure, chamber to sa id third', chamber and consequentlyto one side offY said second member,A the oppositepside .of said second `'member being subjected toa pressure less y than either of the individual pressures .of said small pressure differential, said third chamber having a restricted fluid pressure leakage path therefrom, and `means responsive to the pressure.vv

diierential across said second member.` Y

3, Apparatus for transforming a small pressure than said first diaphragm and extending across said third chamber, means extending through an opening in said partition and connecting said diaphragms for joint movement, a valve element movable by said connecting means and cooperating with said opening for controlling the transmission of pressure from said high pressure chamber to said third chamber and consequently 6 to one side of said second iiexibie diaphragm, the other side of said second -exible diaphragm being subjected to atmospheric pressure, said third chamber having a restricted atmospheric vent, and a movable member responsive to the pressure differential across said second diaphragm.

FRANCIS J. WI-EGAND. 

